The rationale of this project is to develop a method to monitor the expression levels of a large number of genes in various experimental conditions and to understand global changes of gene expression patterns in development and aging. The systematic analysis of expression patterns of a large number of genes is rapidly becoming the method of choice for many laboratories to understand biological systems. Accordingly, the demand for high quality cDNA libraries and cDNA microarrays is increasing. The goals of this research project are to collect mouse cDNA clones and prepare cDNA microarrays containing as many mouse genes as possible. Previously we assembled and released two non-overlapping mouse gene sets: NIA Mouse 15K cDNA Clone Set, containing ~12,000 unique cDNA clones, and NIA Mouse 7.4K cDNA Clone Set, containing ~7400 unique cDNA clones. These clone sets have been freely distributed to the research community. During this period, we have continued to generate cDNA libraries and obtain cDNA sequences. Furthermore, we have developed a glass-slide microarray platform containing in situ-synthesized 60-mer oligonucleotide probes representing approximately 22,000 unique mouse transcripts, assembled primarily from sequences of stem cell and embryo cDNA libraries. We have optimized RNA labeling protocols and experimental designs to use as little as 2 ng total RNA reliably and reproducibly. At least 98% of the probes contained in the microarray correspond to clones in our publicly-available collections, making cDNAs readily available for further experimentation on genes of interest. Future plans include the expansion of the set of unique genes by sequencing more cDNA clones from various embryonic collections, and the preparation and use of cDNA microarrays from the expanded set of unique genes.